Ultrasonic meters are employed in a number of applications and industries for measuring fluid flow. One area where ultrasonic meters find particular usefulness is in the oil and gas industries. After hydrocarbons are removed from the ground, for example, the fluid stream (e.g., crude oil, natural gas) is transported from place-to-place via pipelines. It is thus desirable to know with accuracy the amount of fluid flowing through a pipeline, and particular accuracy is demanded when the fluid changes hands or is subject to a “custody transfer.”
Ultrasonic flow meters, for example, may be used to measure the amount of fluid flowing in a pipeline, and ultrasonic flow meters have sufficient accuracy to be used in custody transfer. The value of gas “changing hands” at the point of custody transfer in a high volume natural gas pipeline may amount to a million dollars or more in a single day. For this reason, manufacturers attempt to make ultrasonic meters that are not only very accurate, but also reliable in the sense that the mean time between failures is large.
Thus, any advance which increases the reliability of ultrasonic meters, and/or which decreases the time to troubleshoot and repair time after an ultrasonic meter has failed, would provide a competitive advantage in the marketplace.
To improve the accuracy of ultrasonic meters, the use of several paths to cover more information across the entire cross-section of, for example, a pipeline is advantageous. Mostly the paths are selected due to the Gauβ—integration method, which results in fixed positions and weighting values for each path. It is well known that a crosstalk between different paths can be used to increase the number of originally designed paths. Unfortunately, these additional paths are usually not at the right position to increase the knots of the Gauβ method.
Applying velocity profile descriptions such as potential-law or log-law may overcome this limitation and an exact integration along the reconstructed velocity distribution may result in a higher accuracy as the simple Gauβ method. There are other limitations as well, due to a rather weak propagation of ultra sound in natural gas, normal disc piezo elements are used generating a rather strong beam perpendicular to the piezo plane. The beam aperture of these transducers is rather small. Therefore, a crosstalk between the individual paths is very weak and rarely not applicable for the general measuring range.